Next generation sequencing technology can provide enormous amounts of sequence information from a relatively small sample, such as a sample of nucleic acid (e.g., mRNA) from a single cell. However, it can be difficult to extract quantitative information regarding the absolute or relative abundance of nucleic acids in a sample. In some cases, the attachment of unique molecular identifiers (UMIs), such as unique oligonucleotide barcode sequences, to target nucleic acids, and detection of such UMIs during sequencing, can allow estimation of absolute or relative abundance of target nucleic acids in a sample.